Control of Microbial Growth How to kill them once you grow them

The Control of Microbial Growth Sepsis refers to microbial contamination. Sepsis refers to microbial contamination. Asepsis is the absence of significant contamination. Asepsis is the absence of significant contamination. Aseptic surgery techniques prevent microbial contamination of wounds. Aseptic surgery techniques prevent microbial contamination of wounds.

Sterilization: Removal of all microbial life Sterilization: Removal of all microbial life Commercial Sterilization: Killing C. botulinum endospores Commercial Sterilization: Killing C. botulinum endospores Disinfection: Removal of pathogens Disinfection: Removal of pathogens Antisepsis: Removal of pathogens from living tissue Antisepsis: Removal of pathogens from living tissue Degerming: Removal of microbes from a limited area Degerming: Removal of microbes from a limited area Sanitization: Lower microbial counts on eating utensils Sanitization: Lower microbial counts on eating utensils Biocide/Germicide: Kills microbes Biocide/Germicide: Kills microbes Bacteriostasis: Inhibiting, not killing, microbes Bacteriostasis: Inhibiting, not killing, microbes Terminology

Filtration removes microbes Filtration removes microbes Low temperature inhibits microbial growth Low temperature inhibits microbial growth Refrigeration Refrigeration Deep freezing Deep freezing Lyophilization Lyophilization High pressure denatures proteins High pressure denatures proteins Desiccation prevents metabolism Desiccation prevents metabolism Osmotic pressure causes plasmolysis Osmotic pressure causes plasmolysis Physical Methods of Microbial Control

Filter Sterilization

Moist Heat

Radiation damages DNA Radiation damages DNA Ionizing radiation (X rays, gamma rays, electron beams) Ionizing radiation (X rays, gamma rays, electron beams) Nonionizing radiation Nonionizing radiation UV UV Microwaves kill by heat; not especially antimicrobial Microwaves kill by heat; not especially antimicrobial Physical Methods of Microbial Control

Radiation

Evaluating a disinfectant Evaluating a disinfectant Use-dilution test Use-dilution test 1. Metal rings dipped in test bacteria are dried 2. Dried cultures placed in disinfectant for 10 min at 20°C 3. Rings transferred to culture media to determine whether bacteria survived treatment Chemical Methods of Microbial Control

Figure 7.6 Evaluating a disinfectant Evaluating a disinfectant Disk-diffusion method Disk-diffusion method

Types of Disinfectants Figure 7.7 Phenol Phenol Phenolics. Lysol Phenolics. Lysol Bisphenols. Hexachlorophene, Triclosan Bisphenols. Hexachlorophene, Triclosan Disrupt plasma membranes Disrupt plasma membranes

Biguanides Biguanides Chlorhexidine Chlorhexidine Disrupt plasma membranes Disrupt plasma membranes Types of Disinfectants

Halogens. Iodine, Chlorine Halogens. Iodine, Chlorine Oxidizing agents Oxidizing agents Bleach is hypochlorous acid (HOCl) Bleach is hypochlorous acid (HOCl) Types of Disinfectants

Table 7.6 Alcohols Alcohols Ethanol Ethanol isopropanol isopropanol Denature proteins, dissolve lipids Denature proteins, dissolve lipids

Heavy Metals. Ag, Hg, Cu Heavy Metals. Ag, Hg, Cu Oligodynamic action Oligodynamic action Denature proteins Denature proteins Types of Disinfectants

Surface-Active Agents or Surfactants Surface-Active Agents or Surfactants Types of Disinfectants SoapDegerming Acid-anionic detergents Sanitizing Quarternary ammonium compounds Cationic detergents Bactericidal, Denature proteins, disrupt plasma membrane

Chemical Food Preservatives Chemical Food Preservatives Organic Acids Organic Acids Inhibit metabolism Inhibit metabolism Sorbic acid, benzoic acid, calcium propionate Sorbic acid, benzoic acid, calcium propionate Control molds and bacteria in foods and cosmetics Control molds and bacteria in foods and cosmetics Nitrite prevents endospore germination Nitrite prevents endospore germination Antibiotics. Nisin and natamycin prevent spoilage of cheese Antibiotics. Nisin and natamycin prevent spoilage of cheese Types of Disinfectants

Aldehydes Aldehydes Inactivate proteins by cross-linking with functional groups (–NH 2, –OH, –COOH, —SH) Inactivate proteins by cross-linking with functional groups (–NH 2, –OH, –COOH, —SH) Glutaraldehyde, formaldehyde Glutaraldehyde, formaldehyde Types of Disinfectants

Gaseous Sterilants Gaseous Sterilants Denature proteins Denature proteins Ethylene oxide Ethylene oxide Types of Disinfectants

Peroxygens Peroxygens Oxidizing agents Oxidizing agents O 3, H 2 O 2, peracetic acid O 3, H 2 O 2, peracetic acid Types of Disinfectants

Microbial Characteristics and Microbial Control Figure 7.11

Bacterial populations die at a constant logarithmic rate. Bacterial populations die at a constant logarithmic rate. Figure 7.1a

Number of microbes Number of microbes Environment (organic matter, temperature, biofilms) Environment (organic matter, temperature, biofilms) Time of exposure Time of exposure Microbial characteristics Microbial characteristics Effectiveness of antimicrobial treatment depends on: Figure 7.1b

Microbial Characteristics and Microbial Control Chemical agent Effectiveness against EndosporesMycobacteria PhenolicsPoorGood QuatsNoneNone ChlorinesFairFair AlcoholsPoorGood GlutaraldehydeFairGood